Method of enhancing electrical conduction in gallium-doped zinc oxide films and films made therefrom

ABSTRACT

A method of producing gallium-doped zinc oxide films with enhanced conductivity. The method includes depositing a gallium-doped zinc oxide film on a substrate using a pulsed laser and subjecting the deposited gallium-dope zinc oxide film to a post-treatment effecting recrystallization in the deposited film, wherein the recrystallization enhances the conductivity of the film. Another method of producing gallium-doped zinc oxide films with enhanced conductivity. The method includes the steps of depositing a gallium-doped zinc oxide film on a substrate using a pulsed laser and subjecting the deposited gallium-dope zinc oxide film to an ultraviolet laser beam resulting in recrystallization in the film, wherein the recrystallization enhances the conductivity of the film. A film comprising gallium-doped zinc oxide wherein the film contains a recrystallized grain structure on its surface.

CROSS REFERENCE TO RELATED APPLICATIONS

The present U.S. patent application is a divisional of U.S. patentapplication Ser. No. 16/033,669 filed Jul. 12, 2018, which is related toand claims the priority benefit of U.S. Provisional Patent ApplicationSer. No. 62/532,186 filed Jul. 13, 2017, the contents of which arehereby incorporated by reference in their entirety into the presentdisclosure.

TECHNICAL FIELD

This disclosure relates to methods of improving the electricalconductivity of gallium-doped zinc oxide (GZO) films, especiallytransparent GZO films.

BACKGROUND

This section introduces aspects that may help facilitate a betterunderstanding of the disclosure. Accordingly, these statements are to beread in this light and are not to be understood as admissions about whatis or is not prior art.

Transparent conducting oxide (TCO) films, achieving both electricalconduction and optical transparency, are critical in many large consumeroptoelectronic devices such as flat panel displays, photovoltaic cells,light emitting diodes and electrochromic windows. Generally, these majorapplications require TCO exhibiting electrical resistivity less than10⁻³ Ω·cm while transparency is more than 80% in visible (Vis) andnear-infrared region (NIR). Until recently, over 90% mainstream marketof TCOs were dominated by indium tin oxide (ITO), whose resistivityapproaches 10⁻⁴ Ω·cm. However, due to the toxicity, scarcity andescalating cost of indium, there are urgent needs to seek alternativeTCO films.

Zinc oxides (ZnO) have drawn considerable attention for the last threedecades as a promising substitute for ITO, since it is non-toxic,abundant and inexpensive. And as an II-VI wide band gap (3.34 eV)semiconductor, ZnO exhibits high Vis and NIR transparency. However, pureZnO has high resistivity, which could be decreased by controllablen-type doping with group III elements. And also un-doped ZnO thin filmsalso show instable electrical properties, resulting from thechemisorption of oxygen at the surface and grain boundaries, which leadsto higher resistivity. The properties of the films can be stabilized byextrinsic dopants. Among n-type dopant group III elements, aluminum (Al)and Gallium (Ga) were the most widely used. Ga dopant attracts moreattention due to Ga—O has similar ionic (0.62 vs. 0.74 A) and covalentradii (1.26 vs. 1.25 A) as compared to Zn—O, meaning a highly Ga dopedZnO could be achieved without substantial lattice deformation.

Ga doped ZnO (GZO) is currently under investigation and development toreplace ITO as a transparent conductive coating. To manufacture a GZOfilm, usually physical vapor deposition (PVD) was utilized to pursuehigh electron conductivity. Various deposition techniques are applied toprepare GZO films, such as sputtering, ion beam assisted deposition(IBAD), atomic layer deposition (ALD) and pulsed laser deposition (PLD),most of them mainly operating under vacuum. On the other hand, there aresome reports of depositing GZO by low temperature PVD for opticaldevices or solution based sol-gel fabrication, but poor optoelectronicproperties were obtained. The electrical conductivity of GZO film couldnot exceed 4×10⁻⁴ Ω·m, especially for low thickness (<200 nm) films withhigh optical transparency.

Hence there is an unmet need to improve the electrical conductivity ofGZO films deposited, so that GZO films can compete with ITO films interms of conductivity.

SUMMARY

A method of producing gallium-doped zinc oxide films with enhancedconductivity is disclosed. The method includes the steps of depositing agallium-doped zinc oxide film on a substrate using a pulsed laserdeposition technique, and subjecting the deposited gallium-dope zincoxide film to a post-treatment capable of resulting in recrystallizationin the deposited gallium-doped zinc oxide film, wherein therecrystallization results in a gallium-doped zinc oxide film with aconductivity higher than the conductivity of the gallium-doped zincoxide film deposited on the substrate pulsed laser deposition technique.Examples of substrates suitable for the method of this disclosureinclude but not limited to quartz, silicon, and sapphire.

Another method of producing gallium-doped zinc oxide films with enhancedconductivity is disclosed. The method includes the steps of depositing agallium-doped zinc oxide film on a substrate using a pulsed laserdeposition technique; and subjecting the deposited gallium-dope zincoxide film to a ultraviolet laser beam resulting in recrystallization inthe deposited gallium-doped zinc oxide film, wherein therecrystallization results in a gallium-doped zinc oxide film with aconductivity higher than the conductivity of the gallium-doped zincoxide film deposited on the substrate using the pulsed laser depositiontechnique.

A film comprising gallium-doped zinc oxide wherein the film contains arecrystallized grain structure on its surface is disclosed.

BRIEF DESCRIPTION OF DRAWINGS

Some of the figures shown herein may include dimensions. Further, someof the figures shown herein may have been created from scaled drawingsor from photographs that are scalable. It is understood that suchdimensions or the relative scaling within a figure are by way ofexample, and not to be construed as limiting.

FIG. 1 is a schematic representation of the UV laser recrystallizationof deposited GZO films as a post treatment according to this disclosure.

FIG. 2A shows the COMSOL Multiphysics® simulation set up, with EM moduleto simulate laser-mater interaction and HT module to simulate heattransfer occurs in GZO film and substrate.

FIG. 2B shows results of simulation demonstrating that laser selectiveheating occurs at 45 ns simulation time, in which thermal energy wasmainly absorbed by GZO film rather than glass substrate due to highabsorption coefficient.

FIG. 2C shows temperature evolution of GZO film top surface during lasercrystallization with single pulse delivery.

FIG. 2D shows temperature distribution along depth (160 nm GZO film to−300 nm substrate) at simulation time of 45 ns and 600 ns for singlepulse delivery.

FIG. 2E shows SEM surface morphology of as-deposited GZO film.

FIG. 2F shows SEM surface morphology of Laser crystallized GZO film.

FIGS. 3A through 3H show atomic force microscope (AFM) images of grainmorphology and surface roughness of GZO film after lasercrystallization.

FIG. 4A shows θ-2θ XRD patterns of GZO films as-deposited by PLD andprocessed by Laser at 105.6 mJ/cm², 113.7 mJ/cm² with 10 pulses and 200pulses, respectively.

FIG. 4B shows FWHM and grain size characterization of GZO filmsas-deposited and processed by post laser crystallization.

FIG. 4C shows laser parameter dependence of Hall measurements collectedelectron mobility.

FIG. 4D shows laser parameter dependence of Hall measurements collectedsheet resistance.

FIG. 5 shows influence of laser crystallization on transmittance.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thedisclosure, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of thedisclosure is thereby intended.

In this disclosure, a post-treatment of GZO films produced by PLDmethods is described as a means to enhance the electrical conductivityof the deposited GO films. In experiments leading to this disclosure,Ultra Violet (UV) laser crystallization was employed as a post treatmentmethod GZO films produced by PLD methods.

FIG. 1 is a schematic representation of the UV laser recrystallizationof deposited GZO films as a post treatment according to this disclosure.Referring to FIG. 1, pulsed laser deposition was used to coat Wurtzitestructure Zinc Oxide film onto a glass substrate, with gallium dopantintegrated in one source. After pulsed laser deposition, a pulsed UVLaser was scanning on the GZO film with shaped square beam and top-hatprofile with size of 8×8 mm and enabled translations along both X and Yaxis to boost the process efficiency. As shown, the laser generation,intensity, scanning path and beam size could be integrated into computeraided design program for potential digital manufacturing. After UV lasercrystallization, the treated film could be characterized for qualityanalysis, device fabrication and practical application. During UV laserscanning, each UV laser pulse was able to introduce a localized hightemperature field from photo energy absorption, because the band gap ofGZO film (˜3.6 eV) is lower than the photo energy of Excimer Laser (5eV). This UV laser pulse induced heat treatment would lead tomicrostructure change and physical property improvement afterwards asdescribed in this disclosure.

Laser crystallization experiments were carried out on room temperaturepulsed laser deposition (PLD) samples. Before deposition, a 50.4 mmdiameter, 0.33 mm thick, (0001) orientation sapphire substrate wascleaned by acetone, methanol, and DI water in an ultrasonic cleaner for5 minutes each, sequentially. Then the sapphire substrate was put into ahigh vacuum chamber with a base pressure of 4.0×10⁻⁶ Torr. In thischamber ZnO (99.99%) and 2% Ga2O3-doped zinc oxide (AZO) targets with 50mm diameters were ablated by a KrF excimer laser (λ of 248 nm with τ of25 ns). The target-substrate distance was fixed at 80 mm. Targets andsubstrates rotated at 7 and 5 RPM, respectively. A 50 nm thick i-ZnOfilm (‘i’ means intrinsic, undoped) was deposited on the sapphiresubstrate at a laser fluence of 1.5 J/cm2, repetition rate (RR) of 10 Hzfor 20 minutes, and then 200 nm thick Al—ZnO was deposited at laserfluence of 0.5 J/cm2, RR of 5 Hz for 90 minutes. Finally a 250 nm thickAZO film was deposited at laser fluence of 0.5 J/cm2, RR of 5 Hz for 90minutes. Oxygen pressure was set to be 150 and 1 mTorr for i-ZnO and GZOfilms, respectively.

After PLD, the sample was transferred into a 10 mTorr vacuum chamber forthe UV laser crystallization process. The same excimer laser was usedwith RR of 10 Hz. The laser beam was shaped to a square, top-hat profile(8×8 mm). The sample was placed on a motorized stage which enablestranslations along both X and Y-axes as shown in FIG. 1. Laserintensities used in the crystallization experiments ranged from 120 to200 mJ/cm2. The laser pulse number (N) used ranged from 10 to 200. Afterthe laser crystallization, field emission scanning electron microscopy(FE-SEM) was used to measure the thickness of the AZO film viacross-section; top FE-SEM imaging was used to observe the surfacestructure. X-ray diffraction (XRD) was used to determine the AZO film'scrystallinity and internal stress. Electrical resistivity and carriermobility and concentration were measured by the Hall Effect with the Vander Pauw method. Optical transmittance spectra were measured by Lambda950 ultraviolet-visible and infrared spectrophotometers.

In order to understand the laser heating process, COMSOL Multiphysics®was applied to simulate the laser energy absorption. FIG. 2A shows theCOMSOL Multiphysics® simulation set up, with EM module to simulatelaser-mater interaction and HT module to simulate heat transfer occursin GZO film and substrate. The electromagnetic module (EM) was used tosimulate Laser irradiation, and the heat transfer module (HT) was usedto describe the temperature increase in GZO polycrystalline film duringa single laser pulse delivery. Laser beam is assumed to be in thefundamental mode with wavelength of 248 nm for crystallization process.Primary controlling parameters are laser pulse energy (E), pulseduration (τ), and beam radium (γ). The spatial distribution of laserpulse could be written as equation (1):

$E = {E_{o} \cdot {\exp \left\lbrack {{- 2}\left( {\frac{x^{2}}{r^{2}} + \frac{y^{2}}{r^{2}}} \right)} \right\rbrack}}$

In this equation, E_(o) represents the central pulsed energy of laserbeam, and x, y are coordinates. Temporal distribution of the laser isrepresented by normalized Weibull function, which could manipulate thepulse duration and power by modifying its shape factors. The incidentlaser heating was induced by near-field scattering occurring onpolycrystalline GZO structure, which can be depicts by resistive heating(Q_(RH)), which could be expressed in equation (2):

Q _(RH)=½Re{σEE*−jωED*}

The governing equations in the EM module in this study are Ampere's lawwith Maxwell's Correction and Faraday's law of induction as shown inequation (3):

${{\int{J \cdot {EdV}}} + {\oint{\left( {E \times H} \right) \cdot {nds}}}} = {- {\oint{\left( {{E\frac{\partial D}{\partial t}} + {H\frac{\partial B}{\partial t}}} \right)dV}}}$

Due to the conservation of energy for the electromagnetic filed, wherethe first term and second term on left hand side represent the resistivelosses and radiative losses, respectively. During resistive heating, asheat transfer occurs, temperature (T) would form in the system. Atypical T field is given by solving a coupled HT module with Q_(RH) asthe heating source. The heat transfer equation is governed by equation(4):

$Q_{RH} = {{{\rho \left( {X,T} \right)}{c_{\rho}\left( {X,T} \right)}\frac{\partial{T\left( {X,t} \right)}}{\partial t}} - {\nabla\left\lbrack {{\kappa \left( {X,T} \right)}{\nabla{T\left( {X,T} \right)}}} \right\rbrack} + {{\rho \left( {X,T} \right)}{c_{\rho}\left( {X,T} \right)}v_{s}{\nabla{T\left( {x,t} \right)}}}}$

Equation (2), (3) and (4) are then numerically solved in coupled EMmodule and HT module as shown in FIG. 2A. Laser parameters, materialsproperties and film properties are set as essential input in thesimulation. FIG. 2B shows results of simulation demonstrating that laserselective heating occurs at 45 ns simulation time, in which thermalenergy was mainly absorbed by GZO film rather than glass substrate dueto high absorption coefficient. Referring to FIG. 2B, heat energy wasmainly absorbed by the GZO layer due to higher absorption coefficientcomparing to glass substrate. FIG. 2B represents the temperaturedistribution at the simulation time of 45 ns, in which heat transferinto bottom glass substrate is still insufficient. The highesttemperature in GZO film reaches 1500 K, while low temperature less than600 K was observed in substrate. However, heat transfer occurs then dueto temperature gradient in the GZO-substrate interface.

FIG. 2C shows temperature evolution of GZO film top surface during lasercrystallization with single pulse delivery. The result of one laserpulse irradiation and afterwards were represented in FIG. 2C. Referringto FIG. 2C, the temperature of GZO film increases to 800-1200K in 45 nsdepending on laser intensity of 120-200 mJ cm⁻², respectively. Then thetemperature of the GZO would be lowered by thermal dissipation, asdemonstrated at 600 ns simulation time, before subsequent Laser pulsedelivery. Then the temperature of the GZO would be lowered by thermaldissipation, as demonstrated at 600 ns simulation time, beforesubsequent Laser pulse delivery. This fast heating and following thermaldissipation also could be demonstrated by FIG. 2D, in which thetemperature distribution over GZO film—substrate interface was recorded.Referring to FIG. 2D, in simulation time of 45 ns, thermal energyexchange from laser beam to GZO film governs. GZO film located fromdepth of 0 to 160 nm shows apparent elevated temperature (1000 to1200K). However, when depth goes from 0 to −300 nm for substrate, asharp decrease to room temperature (300K) was observed. Thisdiscontinuous circumstance renders the fact of laser induced selectiveheating. On the other side, thermal dissipation is able to transfer heatinto substrate across interface drive by high temperature gradient. Thisis also demonstrated in FIG. 2D by simulation result in 600 ns in whichboth GZO film and substrate swing around 600K. This fast thermaldissipation indicates a fast cooling process of GZO film after initialselective laser heating. Therefore, multiple laser pulse shinning withrepeatable heating-cooling process is able to drive microstructurechange of target film, similarly to abnormal grain growth in solidrecrystallization process. FIGS. 2E and 2F show the top view FESEM imageof the Laser scanned film comparing to as deposited film, as thermalenergy continues along multi laser pulse delivery (200 pulses in thisimage), the polycrystalline microstructure tends to reform large grainsand faceted boundaries. Comparing untreated (FIG. 2E) to treated (FIG.2F), it is found that the crystallized film is more compact andcontinuous, implying the crystallinity of the GZO film has beensignificantly enhanced.

FIGS. 3A through 3H show atomic force microscope (AFM) images of grainmorphology and surface roughness of GZO film after lasercrystallization. The grain structure before laser crystallization wasshown as nanoparticles weak-linked together after PLD (FIGS. 3A and 3D.After laser crystallization under laser fluence of 105.6 mJ/cm², thegrain boundary between the nanoparticles are much better connected witheach other. With the laser pulse number (p) increases from 10p to 50pand 200p, the grain structure become denser. The average roughnessreduces significantly from 1.45 nm to 0.914 nm after 50p, whichcontribute to less optical scattering of the thin film. As laser fluenceincreases to 113.7 mJ/cm², the grain size increases more significantlythan under 105.6 mJ/cm². Clear grain boundary can be seen after lasercrystallization with 50p and 200p, while the grain structure isoptimized with 50p.

FIG. 4A shows θ-2θ XRD patterns of GZO films as-deposited by PLD andprocessed by Laser at 105.6 mJ/cm², 113.7 mJ/cm² with 10 pulses and 200pulses, respectively. The crystallinity modification of GZO film couldbe verified by X-Ray Diffraction Patterns (XRD) as shown in FIG. 4A.Typical peak located at 20=34.6° is well indexed to Wurtzite Zinc Oxidecrystal planes of (002). Comparing to signals before lasercrystallization, it is clear seen that (002) peak of GZO film achievemuch higher intensity after multiple laser pulse delivery (200 pulses),implying enlarged grain size and textured crystal orientation. Furtherexploring of the structural modification on GZO film was characterizedby calculating the Full Width Half Maximum (FWHM) and the grain sizeaccording to XRD peaks. The FWHM was measured by the Lorenz fit of the(002) peak, while grain size could be drawn from Bragg's Equation withFWHM as the input. FIG. 4B illustrates the FWHM and grain size of theGZO film as a function of laser processing conditions. Apparently withmultiple laser pulse delivery for both laser intensity of 105.6 mJ/cm2and 113.7 mJ/cm2, the FWHM show much narrower FWHM and grain show muchlarger size comparing to as-deposited film. These results are in goodagreement with FIG. 3 A through 3H in which large grain and facetedboundaries are formed combining with homogeneous and continuous surface.

In order to assess the effects of crystallization on GZO film electricalperformance, hall measurement was carried out. It is well known, withsmall size grain merged and larger size grain formed, it isstraightforward to draw that grain boundary density was decreased.What's more, since the grain shape changed to facetted and surfacecompacted, the inter grain defects like voids, gaps and discontinuitydecrease, which originally may create energy levels in the band gap thattend to trap the free electrons and decrease their lifetime. Both lowergrain boundary density and less electron traps at boundaries are able todiminish the grain boundary barrier scattering and boost the electronmobility cross boundaries, which contribute to or dominate thepolycrystalline GZO film mobility. FIGS. 4C and 4D show laser parameterdependence of Hall measurements collected electron mobility and sheetresistance respectively. As demonstrated in FIGS. 4C and 4D, theelectrical properties of GZO films as a function of laser parameters,detected by Hall Effect Measurement was plotted. After thecrystallization, a strong increase in mobility and decrease in sheetresistance are observed for all different Laser parameters as shown inFIGS. 4C and 4D. The as deposited GZO film performs a hall mobility of16 cm2 V-1 s-1, on contrast, the hall mobility increases to ˜20 cm2 V-1s-1 with 10 laser pulses delivery and ˜22 cm2 V-1 s-1 with 200 laserpulses delivery.

In order to delve into the mechanism of electron mobility improvement,the electron's mean free path l could be calculated using the followingequation 5:

$l = {\frac{h}{2e}\left( \frac{3N}{\pi} \right)^{\frac{1}{3}}\mu}$

Where h is the Plank's constant, e is the electron charge, N is thecarrier concentration and μ is the hall mobility. Inputting hallmeasurement values in table 1, the mean free path of the carriers foras-deposited GZO film could be calculated as 3.1 nm, which is in thesame range of grain size shown in FIG. 4B. This indicates the electronmobility inside polycrystalline GZO film is mainly dominated by grainboundary scattering mechanism. To analyze the grain boundary scatteringdominated mobility μ_(g) enhancement of GZO film after lasercrystallization, the polycrystalline structure and energy level could bereferred. The grain boundary density is determined by grain size L whilethe scattering intensity at grain boundaries is determined by energypotential barrier height Φ_(b). The latter one is controlled by electrontrap density (N_(t)) and the free electron concentration (N_(eff)). Someresearchers extended models in the literature on the basis of the firstapproximation to describe the energy potential barrier at grain boundaryas shown in equation (6) below which εϵ₀ is the static dielectricconstant, m* is the electron effective mass and e is the elementarycharge.

$\mu_{g} = {{\mu_{0}{\exp \left( {- \frac{\Phi_{B}}{kT}} \right)}} = {\frac{eL}{\sqrt{2\pi m^{*}kT}}{\exp \left( {- \frac{e^{2}N_{t}^{2}}{8{kT}\; ɛ\; \epsilon_{0}N_{eff}}} \right)}}}$

The basic result of this equation is based on electrons transportthrough grain boundary by thermionic emission over the barrier, takinginto account of electron traps as a depletion region formed on eitherside of the grain boundary barrier. Based on equation (6), the electronmobility inside GZO film is mainly dominated by grain size L and electrotrap density at grain boundaries N_(t). Thereby, after lasercrystallization, the increased mobility by hall measurement could beused for reverse derivation. As derived with inputting of hall mobilityof 20 and 22 cm² V⁻¹ s⁻¹ into equation (5), the mean free path ofelectrons should be 3.8 and 4.2 nm, respectively. This value is muchhigher comparing to the measured grain size in FIG. 4B (3.2 and 3.6 nm),implying the larger grain formation is not the only reason for electronmobility increase. Thus, there must be decrease of electron trap densityN_(t) contributing to electron mobility enhancement in GZO film afterlaser crystallization. The decrease of electron trap density attributesto both removal of extended defects (mid-band energy level) anddesorption of oxygen species at grain boundaries. Desorption of oxygenspecies by UV Laser exposure would release free carriers from trapswhich is stated by prior report. Subject to current series of samples,this could be demonstrated by a moderate increase of carrierconcentration after laser as shown in Table 1 below.

Table 1 Laser crystallization conditions on GZO films and the derivedHall measurement performance. laser intensity pulses R_(sheet) (Ω/sq) ρ(Ω · cm) μ (cm²/Vs) N_(eff) (cm³) 0  0 p 33.23 5.12 × 10⁻⁴ 16.1 −7.56 ×10²⁰ 105.6 mJ/cm²  10 p 26.98 4.05 × 10⁻⁴ 20.1 −7.66 × 10²⁰ 105.6 mJ/cm²200 p 21.95 3.29 × 10⁻⁴ 21.8 −8.70 × 10²⁰ 113.7 mJ/cm²  10 p 27.18 4.08× 10⁻⁴ 20.5 −7.46 × 10²⁰ 113.7 mJ/cm² 200 p 21.59 3.24 × 10⁻⁴ 22.1 −8.73× 10²⁰

The electron mobility increase would result in sheet resistancedecreases from 33 Ω/sq to 21 Ω/sq, when multiple laser pulses weredelivered to GZO film with optimal laser intensity. As demonstrated inFIG. 4D, the sheet resistance of GZO films varies as a function of laserparameter. Both higher laser intensity and multiple laser pulses wouldcontribute to low sheet resistance. The optimal laser intensity andpulse number was observed as 113.7 mJ/cm² and 200 pulses. The optimallaser conditions could be varied according to different metal oxide anddifferent substrate, however are straightforward to discover with aseries of experiments. And it should be noted that, althoughconductivity enhancement associates with a strong increase in carriermobility, a moderate increase in carrier concentration also should notbe neglected. This moderate increase of carrier concentration inside GZOfilm not only reflects in sheet resistance decrease but also in opticaltransmittance change.

FIG. 5 shows influence of laser crystallization on transmittance.Referring to FIG. 5, visible-IR transmittance spectrum (with glasssubstrate during measuring) processed GZO films encounter a blue shift.As demonstrated in FIG. 5, the optical transmittance as a function ofwavelength, it is clearly that the optical transmittance encounters aslight blue shift after laser crystallization. The relatively decreasedtransmittance in near-infrared range (700-1200 nm) indicates freecarrier absorption, which is in good agreement with moderate carrierconcentration increase in Table 1. It should be noted that, thetransmittance of current series of samples were all measured with glasssubstrate, which still achieve around 90% transmittance in visiblerange. The high optical transparency and simultaneous low sheetresistance of the laser crystallized GZO film imply a significantlyimproved overall optoelectronic property. Electron mobility vs. freeelectron concentration data for GZO thin films deposited by several highvacuum methods from prior research by twelve groups was studied. Theseprior advancements have achieved highest electrical conductivity ondifferent substrates (polymer, glass and sapphire), which provide acomparison with our results based on laser crystallization. ComparingPLD and followed laser crystallization method in our work with othergroups the Laser crystallized GZO films exhibit high mobility (22 cm²V⁻¹s⁻¹), implying diminishing grain boundary barrier and decreasing grainboundary density. The highest electrical conductivity of current seriesof sample achieves over 3000 S/cm, which performs better than almost allthe prior vacuum methods. Additionally, grain boundary density alsocould be affected by film thickness and crystal growth method whichwould further influence the carrier mobility. And according to equation(6), the grain boundary density influences the grain boundary mobilitywith a linear factor. This supply an explanation that charge mobility inour study is still lower than some high vacuum fabrications. However,considering the 160 nm thick top layer in our work is thinner than prioradvancements, our laser crystallization has potential to achieve evenhigher carrier mobility.

Thus this disclosure describes the method of PLD and followed by Lasercrystallization was explored to deposited transparent and conductive GZOfilms onto glass substrate. This laser induced crystallization techniqueis able to apply ultra-fast post heat treatment (in severalmicro-seconds) to modify GZO films with better structural andoptoelectronics properties, suggesting a potential for large-scalemanufacturing. Multiphysics simulation model coupled laser-materinteraction and heat transfer was utilized to study pulse laser heatingand heat dissipation process. The optimally crystallized GZO filmexhibits low resistivity of ˜3.2×10-4 Ω-cm, high Hall mobility of 22cm2/Vs, and low sheet resistance of 22 Ω/sq. The high transmittance (T)over 90% @550 nm is obtained (with glass substrate). The optoelectronicperformance improved mainly attributes to the polycrystalline film grainboundary modification by UV Laser such as grain boundary densitydecrease and the grain boundary electron traps passivation, asdemonstrated by material characterization results. The ultra-fast andflexible laser treatments have the potential to apply in other metaloxides and other deposition methods, such as sol-gel, printing, andspray-coating.

It should be stressed that in this disclosure Transparent and conductiveGallium doped Zinc Oxide (GZO) films were deposited by pulsed laserdeposition and followed by Laser crystallization. This laser inducedcrystallization technique is able to apply ultra-fast post treatment tomodify GZO films with better structural and optoelectronics properties,suggesting a potential for large-scale manufacturing. A physicalsimulation model coupled laser-mater interaction and heat-transfer wasutilized to study pulse laser heating and heat dissipation process. Thelaser crystallized GZO film exhibits low resistivity of ˜3.2×10⁻⁴ Ω-cm,high Hall mobility of 22 cm²/Vs, and low sheet resistance of 22 Ω/sq.The high transmittance (T) over 90% @550 nm is obtained (with glasssubstrate). The optoelectronic performance improved mainly attributes tothe polycrystalline film grain boundary modification by UV Laser such asgrain boundary density decrease and the grain boundary trap densitypassivation.

Based on the above description, it is an objective of this disclosure todescribe a method of producing gallium-doped zinc oxide films withenhanced conductivity. The method includes the steps of depositing agallium-doped zinc oxide film on a substrate using a pulsed laserdeposition technique, and subjecting the deposited gallium-dope zincoxide film to a post-treatment capable of resulting in recrystallizationof the deposited gallium-doped zinc oxide film, wherein therecrystallization results in a gallium-doped zinc oxide film with aconductivity higher than the conductivity of the gallium-doped zincoxide film deposited on the substrate pulsed laser deposition technique.Examples of substrates suitable for the method of this disclosureinclude but not limited to quartz, silicon, and sapphire.

Based on the above description, it is another objective of thisdisclosure to describe a method of producing gallium-doped zinc oxidefilms with enhanced conductivity. The method includes the steps ofdepositing a gallium-doped zinc oxide film on a substrate using a pulsedlaser deposition technique, and subjecting the deposited gallium-dopezinc oxide film to a ultraviolet laser beam resulting inrecrystallization of the deposited gallium-doped zinc oxide film,wherein the recrystallization results in a gallium-doped zinc oxide filmwith a conductivity higher than the conductivity of the gallium-dopedzinc oxide film deposited on the substrate pulsed laser depositiontechnique. Examples of substrates suitable for the method of thisdisclosure include but not limited to quartz, silicon, and sapphire.

It is also an objective of this disclosure to describe a film comprisinggallium-doped zinc oxide wherein the film contains a recrystallizedgrain structure on its surface. In some embodiments of the film, thefilm exhibits Hall mobility in the range of 20-30 cm² V⁻¹ s⁻¹. In someembodiments of the film, the film has a sheet resistance in the range of15-25 ohms/square. In certain embodiments of the film, the film has anaverage surface roughness in the range of 0.9-2.5 nm. In someembodiments of the film, film has a transmittance of 80%-90% in thevisible light frequency range. It is possible to achieve transmittancehigher than 90% for visible light by fine tuning the processingconditions of the method described above and by optimizing therecrystallization structure which includes grain size and surfaceroughness.

While the present disclosure has been described with reference tocertain embodiments, it will be apparent to those of ordinary skill inthe art that other embodiments and implementations are possible that arewithin the scope of the present disclosure without departing from thespirit and scope of the present disclosure. Thus, the implementationsshould not be limited to the particular limitations described. Otherimplementations may be possible. It is therefore intended that theforegoing detailed description be regarded as illustrative rather thanlimiting. Thus, this disclosure is limited only by the following claims.

1. A method of producing gallium-doped zinc oxide films with enhancedconductivity, the method comprising: depositing a gallium-doped zincoxide film on a substrate using a pulsed laser deposition technique; andsubjecting the deposited gallium-doped zinc oxide film to a posttreatment capable of resulting in recrystallization in the depositedgallium-doped zinc oxide film, wherein the recrystallization results ina recrystallized gallium-doped zinc oxide film with a conductivityhigher than the conductivity of the gallium-doped zinc oxide filmdeposited on the substrate using the pulsed laser deposition technique2. The method of claim 1, wherein the post treatment comprisessubjecting the deposited gallium-doped zinc oxide film to an ultravioletlaser beam.
 3. The method of claim 2, wherein the substrate is one ofquartz, silicon, and sapphire.
 4. The method of claim 2, wherein therecrystallized gallium-doped zinc oxide film contains a recrystallizedgrain structure on its surface, wherein grains of the film containnanoparticles, and grain boundaries between the nano particles of thegrains are faceted, and wherein the film has an average surfaceroughness in the range of 0.9-2.5 nm.
 5. The method of claim 2, whereinthe recrystallized gallium-doped zinc oxide film exhibits Hall mobilityin the range of 20-30 cm² V⁻¹ s⁻¹.
 6. The method of claim 2, wherein therecrystallized gallium-doped zinc oxide film has a sheet resistance inthe range of 15-25 ohms/square.
 7. The method of claim 2, wherein therecrystallized gallium-doped zinc oxide film has a transmittance of80%-90% in the visible frequency range.